The present disclosure is, in particular embodiments, directed to methods and apparatus relating to an adapted fan unit (e.g., fan module with fan, housing, motor, supports, possibly appurtenances) that exhibits improved, perhaps even optimal aerodynamic and/or acoustic performance. Such fan units are normally employed in building ventilation systems.
Air delivery systems for building ventilation may include one or more centrifugal fan units. Such fan units typically are intended to meet specified performance criteria, such as flow, output pressure, input power, and acoustic output. Current practice is to use fans that meet the basic criteria of flow and pressure, but with a compromise of efficiency (whether static or total efficiency) and/or acoustic performance. In many applications, there may be a need for maximum efficiency, but with relaxed acoustic requirements. Conversely, some applications may require minimum noise at the expense of efficiency. At times, this may be due to a desire to use the same size housing for different units that are in fluidic communication (e.g., a supply fan and a return fan, which together, or either alone, is a type of air handling apparatus).
With current fan technology, in particular applications it is not possible to selectively optimize a fan for efficiency or acoustic performance. Typically, mitigation of noise requires the installation of sound traps external to the fan—with a resulting increase in overall air handler length and cost, and a decrease in efficiency. Furthermore, fans are most efficient over a relatively narrow range of the flow-pressure curve, and design flow-pressure conditions may require that a fan be selected outside the region of peak efficiency.
Previous U.S. Pat. Nos. (7,001,140 and 7,357,621) describe methods for increasing the static efficiency of centrifugal fans through proper design of fan housings. Other patents describe installing centrifugal fans in modular acoustically insulated housings to allow installation of arrays of fans in building ventilation applications (e.g. U.S. Pat. No. 8,272,700.) U.S. Pat. No. 7,001,140 is also prior art. Particular embodiments of the inventive technology may leverage that disclosure to allow a variety of fan wheel diameters and linings in an efficient axial discharge housing. That patent's FIG. 15 shows one way of generating an annular output; such housing may be used in particular embodiments of the inventive technology disclosed herein. Note, however, that the momentum diffuser shown in that figure, while certainly usable in such embodiments, is not a required feature thereof.
Prior art centrifugal fans for building ventilation are shown in FIG. 1. Current practice includes unhoused centrifugal 1 or housed fans 2 intended to be installed in arrays of fans. FIGS. 1A and 1B of the instant disclosure are prior art. FIG. 1A shows a standard plenum fan an unhoused centrifugal fan). FIG. 1B shows a centrifugal fan in a box housing; it has no internal flow path and affords no way in which to add vanes 12 or efficiency enhancing acoustic treatment (e.g., lining, treatment). None of the existent prior art describes the tailoring of a fan module or fan unit (which include the outer housing housing) appurtenances to particular efficiency, aerodynamic performance, and/or acoustic performance requirements; in this sense, the invention may involve modular air handling systems.
As relevant background in one application, air handlers (the units that typically provide ventilation air in buildings) typically have two sets of fans that are in fluidic communication—one is the higher pressure fan array (supply fans) that pushes air into the building and the other is a lower pressure fan array (return fans) that pulls air back out of the building. Typically, the supply and return fans need to handle approximately the same volume flow of air, and the static pressure requirements for the return fans is less than that of the supply fans. Fans of a single fan wheel diameter (size) cannot serve as both supply and return fans in a way that maximizes efficiency for the system (or for each fan); indeed, in may applications, a single fan diameter cannot even serve both applications in an efficient manner whatsoever. Certain embodiments of the inventive technology disclosed herein may achieve substantially the same efficiency for each of the fan units that are in fluidic communication by tailoring one or more of such fan units, via, e.g., selection of non-traditionally used wheel sizes, use of acoustic treatment 8, and/or use of fixed vanes 12. Particular embodiments of the inventive technology disclosed herein may allow for optimization of one or more system parameters (e.g., static efficiency and acoustic performance) of fans that are in fluidic communication.